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IPv6 ULA Prefix Generator

Generates an IPv6 Unique Local Address (ULA) prefix per RFC 4193.

How to use

  1. Open the Tool Drawer — click the toolbar button on the IPv6 tab.
  2. Optionally enter a 10-character hex Global ID (40 bits). Leave blank to generate one pseudo-randomly.
  3. Click Generate ULA Prefix.

Output

A /48 prefix starting with fd (the ULA range fc00::/7 with L-bit set). For example:

fd12:3456:789a::/48

The result also shows:

  • The Global ID used
  • Five example /64 subnets derived from the prefix
  • The total number of /64 subnets available within the prefix (65,536 for a /48)

Global ID

The 40-bit global ID is the locally significant portion of the ULA prefix. RFC 4193 recommends deriving it pseudo-randomly so it is globally unique with high probability. You can supply your own value for reproducibility (e.g. to regenerate a prefix from an existing network plan).

Warning

ULA prefixes are not globally routable. They are intended for use within a private network and should not appear in BGP routing tables.

REST API

Generate a ULA prefix programmatically via POST /api/v1/ula.